Originally Posted by mach42006

Hi all, first time poster in need of some input.

I own a 2005 Mazda 3, 2.3L Automatic, purchased used about 4 months ago. It's currently in the shop, and after three days of diagnosis the mechanic wants to replace the computer for a total of $600 (~$300 for the computer itself).

Here's the background info on the problem I'm having with the car. The car has run great since I got it. The Check Engine Light has been on since two weeks after the purchase; the diagnostic test revealed only a O2 sensor, and the mechanic recommended that I don't worry about it. So the light has remained on, and I have not had the O2 sensor replaced. The car ran great up until last weekend. I drove to my destination without any problems. When I got in the car to return home, the AT light came on and the car would only rev to ~2,000RPM. (It did not red-line at 2000, it simply stopped stayed steady at 2000). I checked the transmission fluid, there was only about 1/4 inch on the bottom of the stick, so I added some. Didn't solve the problem, but I drove it home since I was pretty close. It would only go about 20-30mph, shifting when it picked up enough speed. One of my friends recommended I reset the computer, so I did. The AT light did not come back on, however the problem persisted. I'm fairly optimistic it's not a mechanical problem with the transmission. I have never experienced any problems shifting or accelerating, and again, it seemed to run perfectly fine until this problem suddenly occurred.

I took it to the mechanic on Monday. He said he got a code from the computer for the Mass Airflow Sensor. They replaced it but it didn't solve the problem, so they removed it. At that time, the mechanic told me that he was concerned about the computer, since it appeared to be a "salvage" computer and appeared to have water damage. The carfax for the car is clean, fwiw, however the previous owner did make a few minor modifications, though I don't know why he would have replaced the computer.

At that point, with no other codes being registered by the computer, they started a 3 day diagnostic process testing the sensors and the wiring and connections. Throughout the process at various times, the computer registered several codes for various things from the transmission to engine problems, though the codes came and went. Also, the computer didn't register information or codes that it should have throughout the process.

For this reason, the mechanic said he was "as certain as [he] could be" that the computer needs replacing, for the price quoted above. I don't disagree with him, however I fear that the computer is not what is causing the problem above, but simply a means of correctly displaying the cause of the problem above. So that adds up to $600 for the computer, + $xxx for the real problem. I can afford one or the other, but not both.

So to save money, I want to know if it's reasonable for me to be able to purchase and replace the computer myself. I have a few questions about it, though.

-I only have the model number of the computer CURRENTLY in the car, which apparently is not the ORIGINAL computer. Can I purchase ANY 2005 Mazda 3 2.3L Automatic computer?

-Will the computer require programming before it will work? Or is it essentially plug-and-play?

-What is involved in properly replacing the computer? Is it correct that it is beneath the battery?

FWIW, I'm currently looking at this computer:
http://cgi.ebay.com/ebaymotors/ECU-E...ht_2213wt_1118

Thanks a lot for reading. I posted the full situation incase someone has some input on not only replacing the computer, but any other possible causes of the problem. Thanks in advance for any information.